diff --git a/installer/Anonymisation.iss b/installer/Anonymisation.iss
index 3f8b799..e211813 100644
--- a/installer/Anonymisation.iss
+++ b/installer/Anonymisation.iss
@@ -24,6 +24,11 @@ SolidCompression=yes
 WizardStyle=modern
 ArchitecturesAllowed=x64compatible
 ArchitecturesInstallIn64BitMode=x64compatible
+; D8 (Plan 3) : MAJ propre — ferme l'app avant remplacement de l'EXE.
+; AppMutex = gui_v6/single_instance.py:APP_MUTEX_NAME (NE PAS désynchroniser).
+AppMutex=AivanonymAnonymisationV6
+CloseApplications=yes
+RestartApplications=no
 
 [Languages]
 Name: "french"; MessagesFile: "compiler:Languages\French.isl"
diff --git a/tests/unit/test_installer_iss_d8.py b/tests/unit/test_installer_iss_d8.py
new file mode 100644
index 0000000..8fc7d4b
--- /dev/null
+++ b/tests/unit/test_installer_iss_d8.py
@@ -0,0 +1,27 @@
+"""Anti-dérive D8 (Plan 3) : l'installeur GUI doit fermer l'app avant MAJ.
+
+AppMutex DOIT valoir gui_v6.single_instance.APP_MUTEX_NAME (P0-7) — le commentaire
+de single_instance.py:15 exige la synchro. CloseApplications ferme l'app qui
+verrouille l'EXE pendant l'upgrade en place (AppId fixe).
+"""
+from pathlib import Path
+
+from gui_v6.single_instance import APP_MUTEX_NAME
+
+ISS = Path(__file__).resolve().parents[2] / "installer" / "Anonymisation.iss"
+
+
+def test_appmutex_synchronise_avec_single_instance():
+    text = ISS.read_text(encoding="utf-8")
+    assert f"AppMutex={APP_MUTEX_NAME}" in text
+
+
+def test_closeapplications_actif():
+    text = ISS.read_text(encoding="utf-8")
+    assert "CloseApplications=yes" in text
+
+
+def test_appid_fixe_inchange():
+    # L'upgrade en place repose sur l'AppId stable — ne jamais le régénérer.
+    text = ISS.read_text(encoding="utf-8")
+    assert "AppId={{6D11E4F8-26D8-4CFB-9F19-5A81E0637F56}" in text